JP2010039416A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly correct the start time of scanning and the scanning width of laser light beam, accompanying the expansion of a scanning lens due to a temperature variation. <P>SOLUTION: A first BD sensor 101 is installed, at a position where laser light beam L which does not pass through a first scanning lens 83 is detectable in a scanner unit 48. Furthermore, a second BD sensor 102 is installed, at a position where the laser light beam L, which passes through the first scanning lens 83 is detectable. The detection time difference between the time, when the first BD sensor 101 detects the laser light beam L, and the time when the second BD sensor 102 detects the laser light beam L is calculated. A video controller 108 reads correction data stored in a memory 112, on the basis of the detection time difference, and drives and controls an engine controller 110 so as to drive an LD (laser diode) with a timing for cancellation of shift in the start time of scanning and the scanning width due to the expansion of the first scanning lens 83. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for correcting changes in scanning start timing and scanning width of a laser beam accompanying a temperature change.

  Conventionally, there is an image forming apparatus (hereinafter referred to as a laser printer) that applies electrophotographic technology. For example, image formation in a direct transfer type laser printer that directly transfers a developed image onto a sheet is performed as follows. The laser printer includes a photosensitive drum, a charger, an exposure device, a developing device, a transfer device, and the like around each photosensitive drum, and a fixing device and the like on the downstream side of the transfer device in the sheet conveyance direction.

  First, the surface of the photosensitive drum is uniformly charged by a charger. Subsequently, an electrostatic latent image is formed on the surface of the photosensitive drum by the laser beam scanned from the exposure unit. Thereafter, the electrostatic latent image is developed as a toner image with the toner supplied from the developing unit, and the developed toner image is placed on a conveying belt constituting the transfer unit and conveyed to the sheet at a proper timing. It is transferred when passing between the conveyor belt and the photosensitive drum. Then, the image is fixed on the sheet by the fixing device and discharged.

  In this laser printer, the exposure device is provided with a laser light detection sensor (hereinafter referred to as a BD sensor) for adjusting the writing timing for each time when the photosensitive drum is scanned and exposed with laser light to form an electrostatic latent image. It has been. This BD sensor is an element that, when receiving laser light, converts it into an electrical signal and outputs the signal, and the printer controls writing based on this signal.

  The timing at which the laser beam that scans the photosensitive drum by the BD sensor is scanned to the print start position is detected. Further, by synchronizing the scanning of the laser beam and the sheet conveyance timing in the main body of the image forming apparatus, printing without deviation in the writing position on the sheet is performed.

  By the way, the internal temperature of the laser printer changes every moment due to the heat generated by the temperature of the fixing unit and the rotational driving of the rotary polygon mirror provided in the exposure unit. Due to this temperature change, there is a problem in that the lens installed in the exposure device expands, and the scanning start timing of the laser light that is transmitted through the lens and scanned onto the photosensitive drum changes. In particular, since a color laser printer exposes image data of each color to a plurality of photosensitive drums, the scanning position of each color shifts, and a toner image formed based on them is converted into a superimposed image. There was a problem that color misregistration occurred.

  To solve this problem, a technique is known in which two BD sensors are provided and the scanning position is corrected based on the difference in detection time at which each BD sensor detects a laser beam.

That is, two BD sensors are provided at positions where laser beams that pass through two scanning lenses arranged at different positions in the exposure device can be detected, and the difference in detection time between the two BD sensors detecting the laser beams. Ask for. Then, the relationship between the detection time difference between the two BD sensors detecting the laser light and the amount of deviation of each color is obtained in advance experimentally, and the relationship is compared with the actually detected time difference to actually scan. A technique has been proposed in which the amount of deviation of the scanning position of the laser beam is estimated, and the scanning start timing and the scanning width of the laser beam corresponding to the image data for each color are corrected so that the amount of deviation is offset [patent Reference 1].
JP 2007-163765 A

  However, in the above technique, since the two BD sensors are both arranged at positions after the laser light is transmitted through the scanning lens, both of the laser lights reaching the two BD sensors are affected by the expansion of the lens due to temperature changes. Therefore, there is a deviation in detection by each BD sensor. Therefore, neither of the two BD sensors can be used as a reference, and the time difference between the two detection times does not correspond to the magnitude of lens expansion due to a temperature change. For this reason, there is a problem in the correction accuracy of the scan start timing and the scan width.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of highly accurately correcting a temperature change in the apparatus with respect to a scanning start timing and a scanning width of a laser beam scanned on a photosensitive member.

  In order to achieve this object, the invention according to claim 1 is directed to a light source that emits laser light, a deflector that deflects the laser light emitted from the light source, a photoconductor, and the deflected laser light. In the image forming apparatus including a first scanning lens that scans and forms an image on the photosensitive member, first detection means capable of detecting the laser light that does not pass through the first scanning lens, and the first The second detection means provided at a position different from the detection means and capable of detecting the laser light transmitted through the first scanning lens, and the two detection means that change in response to a temperature change, A difference in detection time from when the laser light is detected by the first detection means to when the second detection means detects the laser light, and the photoconductor that changes corresponding to the change in the detection time difference The race above The storage means for storing the correspondence information of the deviation amount of the scanning start timing of the light and the actual detection time difference between the two detection means are measured, and on the photoconductor based on the measurement result and the correspondence information And a correction means for correcting the scanning start timing of the laser beam.

  According to a second aspect of the present invention, there is provided a light source that emits laser light, a deflector that deflects the laser light emitted from the light source, a photosensitive member, and the deflected laser light on the photosensitive member. In an image forming apparatus including a first scanning lens that scans and forms an image, a first detection unit that can detect the laser light that does not pass through the first scanning lens, and a position different from the first detection unit A second detection means that can detect the laser light transmitted through the first scanning lens, and the first detection means of the two detection means that changes in response to a temperature change. The detection time difference from when the laser light is detected until the second detection means detects the laser light, and the laser light on the photoconductor that changes in accordance with the change in the detection time difference. Scan width deviation The actual detection time difference between the storage means for storing correspondence information and the two detection means is measured, and the scanning width of the laser beam on the photoconductor is corrected based on the measurement result and the correspondence information. And a correction means.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the laser beam is converged on the first detection unit in an optical path from the deflector to the first detection unit. Therefore, a converging lens having a plane symmetric with respect to the optical axis in the main scanning direction of the laser beam is provided.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the photoconductor is provided corresponding to the image data for each color, and the correcting means is the photoconductor for each color. The scanning start timing or the scanning width is corrected.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the rotation axis of the deflector is included and the surface is perpendicular to the optical axis of the first scanning lens. A second scanning lens is provided at a position symmetrical to the first scanning lens, and the correction means applies the second scanning lens to the second scanning lens based on the detection result of the laser beam scanned by the first scanning lens. The scanning start timing or the scanning width on the photosensitive member corresponding to the scanned laser beam is corrected.

  The invention according to claim 6 is the invention according to claim 4, wherein a plurality of the scanning lenses are provided, and one of the plurality of scanning lenses does not pass through the scanning lens. The first detection means capable of detecting laser light and the second detection means capable of detecting the laser light transmitted through the scanning lens are arranged, and the scanning lens is used for other scanning lenses. Third detection means capable of detecting transmitted laser light is disposed, and the correction means transmits the other scanning lens based on a detection time difference between the first detection means and the third detection means. The scanning start timing or the scanning width of light on the photosensitive member is corrected.

  The invention according to claim 7 is the invention according to claim 5, wherein a plurality of the scanning lenses are provided, the first detection means and the second detection means are arranged corresponding to each of the scanning lenses. It is characterized by being.

  The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein the scanning lens is an fθ lens.

  The invention according to claim 9 is the invention according to any one of claims 1 to 8, wherein the deflector has a plurality of deflecting surfaces, and the deflecting surface is rotated by rotating the rotating shaft around the rotating shaft. The rotary polygon mirror deflects the incident laser beam.

  According to the first aspect of the present invention, when calculating the detection time difference between the two detection means detecting the laser light, the first detection means detects the laser light that does not pass through the first scanning lens, and the second detection means The detection means detects the laser light passing through the first scanning lens, and the scanning start timing is corrected from the difference between the detection times. In performing the correction, since the laser beam that does not pass through the first scanning lens is detected, the second detection means transmits the first scanning lens after setting a reference detection time that is not affected by temperature change. The difference in detection time from when the laser beam is detected can be calculated. Since the scanning start timing of the laser beam on the photosensitive member is corrected based on the difference in detection time, the deviation of the scanning start timing of the laser beam due to the expansion of the scanning lens can be corrected more accurately.

  According to the second aspect of the present invention, in calculating the detection time difference in which the two detection means detect the laser light, the first detection means detects the laser light that does not pass through the first scanning lens, The second detection means detects the laser light passing through the first scanning lens, and the scanning width is corrected from the difference between the detection times. In performing the correction, since the laser beam that does not pass through the first scanning lens is detected, the second detection means transmits the first scanning lens after setting a reference detection time that is not affected by temperature change. The difference in detection time from when the laser beam is detected can be calculated. Since the scanning width of the laser beam on the photosensitive member is corrected based on the difference in detection time, the deviation of the scanning width of the laser beam due to the expansion of the scanning lens can be corrected more accurately.

  According to the invention described in claim 3, in addition to the effect described in claim 1 or 2, the laser beam is formed on the first detection means by the converging lens having a plane symmetrical to the main scanning direction of the laser beam. Can be converged. Moreover, even if thermal expansion occurs in the converging lens, the detection timing of the reference first detection means does not vary with temperature because it is symmetrical in the main scanning direction. Therefore, even when the laser beam passes through the converging lens, it is possible to correct with high accuracy.

  According to the invention described in claim 4, in addition to the effect described in any one of claims 1 to 3, since the scan start timing or the scan width is corrected for each color image, the images of each color are superimposed. Color shift at the time is prevented.

  According to the invention described in claim 5, in addition to the effect described in any one of claims 1 to 4, the first scanning lens and the second scanning lens include the rotating shaft of the deflector, and The first scanning lens is disposed in a symmetric positional relationship with respect to a plane perpendicular to the optical axis of the one scanning lens. In this arrangement, the scanning start timing of the laser light and the method of changing the scanning width accompanying the expansion of the scanning lens due to temperature rise are also symmetric. Therefore, even if the detection means is arranged only for the first scanning lens and the scanning start timing or the scanning width is corrected based on the detection result, the same applies to the laser light transmitted through the second scanning lens. The scanning start timing or the scanning width can be favorably corrected with this correction amount.

  According to the sixth aspect of the invention, in addition to the effect of the fourth aspect, the third detection means for detecting the laser light transmitted through each scanning lens even if two or more scanning lenses are provided. The expansion of each scanning lens is detected from the difference in detection time from the timing detected by the first detection means, so that the laser light passing through each scanning lens can be corrected. In addition, since only one detection means is required for the second and subsequent scanning lenses, the cost is low.

  According to the seventh aspect of the invention, in addition to the effect of the fifth aspect, by providing the detection means for each scanning lens, the scanning start timing of the laser light accompanying the temperature change of each scanning lens. Since the change in the scanning width can be seen, more accurate correction processing is possible.

  According to the eighth aspect of the invention, in addition to the effect of any of the first to seventh aspects, the expansion of the fθ lens that greatly affects the scanning position can be detected. It can be corrected.

  According to the ninth aspect of the invention, in addition to the effect of any of the first to eighth aspects, the optical system can be efficiently scanned by using a rotating polygon mirror.

[Overall configuration of laser printer]
Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view showing a schematic configuration of a laser printer 2 as an example of an image forming apparatus of the present invention. In the following description, the right side in FIG. 1 is the front side, the upper side is the upper side, and the direction orthogonal to the paper surface is the left-right direction.

  The laser printer 2 is a direct transfer tandem color laser printer, and includes a substantially box-shaped main body casing 4 as shown in FIG. A front cover 6 that can be opened and closed is provided on the front surface of the main casing 4. By opening the front cover 6, the process unit 8 can be drawn forward from the main casing 4. Further, on the upper surface of the main casing 4, a paper discharge tray 10 on which paper P as a recording medium after image formation is stacked is formed.

  A paper feed tray 12 on which paper P for forming an image is loaded is attached to the lower part of the main casing 4 so as to be able to be pulled forward. A paper pressing plate 16 that can be tilted to lift the front end side of the paper P by the bias of the spring 14 is provided in the paper feeding tray 12. In addition, a pickup roller 18 and a separation pad 20 that presses against the pickup roller 18 by biasing a spring (not shown) are provided at a position above the front end of the paper feed tray 12. Further, a pair of paper feed rollers 22 is provided obliquely in front of the pickup roller 18, and a pair of registration rollers 24 is provided thereabove.

  When the uppermost sheet P of the sheet feeding tray 12 is pressed toward the pickup roller 18 by the sheet pressing plate 16 and is sandwiched between the pickup roller 18 and the separation pad 20 by the rotation of the pickup roller 18, 1 is reached. Separated by sheet. The paper P sent out from between the pickup roller 18 and the separation pad 20 is sent to the registration roller 24 by the paper feed roller 22. The registration roller 24 feeds the paper P onto the rear belt unit 26 at a predetermined timing.

  The belt unit 26 is attachable to and detachable from the main casing 4 and includes a conveyor belt 32 that is horizontally installed between a pair of belt support rollers 28 and 30 that are spaced apart from each other. The conveyor belt 32 is an endless belt made of a resin material such as polycarbonate, and is circulated and moved counterclockwise in FIG. 1 when the rear belt support roller 30 is driven to rotate, and is placed on the upper surface thereof. The paper P is conveyed backward.

  Inside the conveyance belt 32, four transfer rollers 38 arranged to face the respective photosensitive drums 36 as an example of the photosensitive member of the present invention included in the image forming unit 34 described later are arranged at regular intervals in the front-rear direction. The conveying belt 32 is sandwiched between the photosensitive drums 36 and the corresponding transfer rollers 38. At the time of transfer, a transfer bias is applied between the transfer roller 38 and the photosensitive drum 36.

  A cleaning roller 40 is provided below the belt unit 26 to remove toner, paper dust, and the like attached to the conveyance belt 32. The cleaning roller 40 is opposed to a metal backup roller 42 provided in the belt unit 26 with the conveyance belt 32 interposed therebetween.

  A predetermined bias is applied between the cleaning roller 40 and the backup roller 42 so that the toner on the conveyor belt 32 is electrically attracted to the cleaning roller 40 side. The cleaning roller 40 is in contact with a metal recovery roller 44 that removes toner and the like adhering to the surface, and the recovery roller 44 has a blade for scraping off the toner and the like adhering to the surface. 46 abuts.

  A scanner unit 48 as a laser scanning device is provided at an upper portion in the main body casing 4, a process unit 8 is provided below the scanner unit 48, and the belt unit 26 is disposed below the process unit 8. Yes.

  The scanner unit 48 performs high-speed scanning on the surface of the corresponding photosensitive drum 36 with the laser light L for each color based on predetermined image data. The configuration of the scanner unit 48 will be described in detail later.

  The process unit 8 includes four image forming units 34 corresponding to each color of black (BK), cyan (C), magenta (M), and yellow (Y), and these image forming units 34 are arranged in the front and rear. Is arranged in. In the present embodiment, the image forming units 34 are arranged in the order of black, cyan, magenta, and yellow from the front side of the laser printer 2.

  Each image forming unit 34 includes a photosensitive drum 36 serving as an image carrier, a scorotron charger 52, a developing cartridge 54 as a developing device, and the like. Further, the process unit 8 includes a frame-shaped frame 58 having four cartridge mounting units 56 arranged in the front-rear direction. Each cartridge mounting part 56 is opened up and down, and each developing cartridge 54 can be attached / detached inside thereof. The frame 58 holds the photosensitive drum 36 of each image forming unit 34 at the lower end position of each cartridge mounting portion 56, and further holds the scorotron charger 52 adjacent to the photosensitive drum 36.

  The photosensitive drum 36 includes a metal drum main body that is grounded, and has a surface layer covered with a positively chargeable photosensitive layer made of polycarbonate or the like.

  The scorotron charger 52 is disposed opposite to the photosensitive drum 36 at a predetermined interval so as not to come into contact with the photosensitive drum 36 at an obliquely upper rear side of the photosensitive drum 36. The scorotron charger 52 uniformly charges the surface of the photosensitive drum 36 to positive polarity by generating corona discharge from a charging wire (not shown) such as tungsten.

  The developing cartridge 54 has a substantially box shape, and a toner storage chamber 60 is provided in an upper portion thereof, and a supply roller 62, a developing roller 64, and a layer thickness regulating blade 66 are provided below the developing cartridge 54. Each toner storage chamber 60 stores positively chargeable nonmagnetic one-component toner of each color of black, cyan, magenta, and yellow as a developer. Each toner storage chamber 60 is provided with an agitator 68 for stirring the toner.

  The toner discharged from the toner storage chamber 60 is supplied to the developing roller 64 by the rotation of the supply roller 62 and is positively frictionally charged between the supply roller 62 and the developing roller 64. Further, the toner supplied onto the developing roller 64 enters between the layer thickness regulating blade 66 and the developing roller 64 as the developing roller 64 rotates, and is further sufficiently frictionally charged here to have a constant thickness. It is carried on the developing roller 64 as a thin layer.

  The surface of the photosensitive drum 36 is uniformly positively charged by the scorotron charger 52 when rotating. Thereafter, exposure is performed by high-speed scanning of the laser light L from the scanner unit 48, and an electrostatic latent image corresponding to an image to be formed on the paper P is formed.

  Next, the electrostatic latent toner formed on the surface of the photosensitive drum 36 when the positively charged toner carried on the developing roller 64 contacts the photosensitive drum 36 by the rotation of the developing roller 64. Supplied to the image. As a result, the electrostatic latent image on the photosensitive drum 36 is visualized, and a toner image having toner attached only to the exposed portion is carried on the surface of the photosensitive drum 36.

  Thereafter, the toner image carried on the surface of each photosensitive drum 36 is transferred to the transfer roller 38 while the paper P conveyed by the conveyance belt 32 passes through each transfer position between the photosensitive drum 36 and the transfer roller 38. The images are sequentially transferred onto the paper P by the applied negative transfer bias. The sheet P having the toner image transferred thereon is then conveyed to the fixing device 70.

  The fixing device 70 is disposed behind the conveying belt 32 in the main body casing 4. The fixing device 70 includes a heating roller 72 that is rotationally driven with a heat source such as a halogen lamp, and a pressure roller 74 that is disposed below the heating roller 72 so as to face the heating roller 72 and is driven to rotate. It has. The fixing device 70 fixes the toner image onto the paper P by heating the paper P carrying the four color toner images while nipping and conveying the paper P by the heating roller 72 and the pressure roller 74.

  Then, the heat-fixed paper P is transported to a paper discharge roller 78 provided on the upper portion of the main body casing 4 by a transport roller 76 disposed obliquely above and rearward of the fixing device 70, and the paper discharge roller 78 described above. The paper is discharged onto the paper discharge tray 10.

In the present invention, the “image forming apparatus” is not limited to a printing apparatus such as a printer (for example, a laser printer), but may be a facsimile apparatus or a multi-function machine having a printer function and a reading function (scanner function). Good. In addition, a direct transfer method for directly transferring an electrostatic latent image for each color formed on the photosensitive drum to a recording medium (paper, OHP sheet, etc.), with each color developer image visualized by a developing unit for each color, Alternatively, any of intermediate transfer systems that indirectly transfer via an intermediate transfer belt may be used. Furthermore, a monochrome printer may be used.
[Configuration of scanner unit]
Next, the configuration and hardware configuration of the scanner unit 48 provided in the laser printer 2 will be described with reference to the drawings. FIG. 2 is a schematic diagram of the scanner unit 48. Among these, the lower diagram is a side cross section viewed from the left side of the scanner unit 48, and the upper diagram is a diagram when the inside of the scanner unit 48 is viewed from above.

  In the drawing, the right side is the front side of the laser printer 2, and the paper P is conveyed by the belt unit 26 from the right to the left of the paper. That is, the left direction of the paper is the conveyance direction of the paper P and the sub-scanning direction on the photosensitive drum 36. In the upper diagram, each reflection mirror is omitted, and the laser beam Lk and the laser beam Ly are developed without being folded back by the reflection mirror, and an optical path optically equivalent to the lower diagram is shown. FIG. 3 is a block diagram showing an electrical configuration for controlling the scanner unit 48.

  As shown in FIG. 2, the scanner unit 48 includes a box-shaped resin housing 80. The scanner unit 48 is a deflector according to the present invention, and has, for example, a six-sided polygon as an example of a rotary polygon mirror. The mirror 82 is provided so as to be rotatable about a rotation axis extending in the vertical direction (rotated and driven counterclockwise in the figure). The housing 80 includes four laser light sources near the left side of the polygon mirror 82, more specifically, laser diodes (hereinafter referred to as “LDk, LDc, LDm, LDy”), a first scanning lens 83 (for example, an fθ lens). A second scanning lens 86 (for example, an fθ lens), a cylindrical lens 84, and the like are provided. Note that fθ is a lens having a property of scanning a laser beam scanned at a constant angular velocity so as to have a constant velocity on the image plane.

  The first scanning lens 83 and the second scanning lens 86 are provided symmetrically on both the front and rear sides of the polygon mirror 82. More specifically, the first scanning lens 83 and the second scanning lens 86 pass through the rotation axis of the polygon mirror 82 and are symmetric with respect to a plane perpendicular to the optical axis of the first scanning lens 83. Is positioned. The first scanning lens 83 and the second scanning lens 86 are slightly wider than the range corresponding to the image forming area on the photosensitive drum 36 in the angular range in which laser light described later is deflected by the polygon mirror. Extends in the scanning direction.

  The LDk is directed to one deflection surface of the polygon mirror 82 located slightly below from the upper position, and is arranged so as to emit the laser beam Lk modulated based on the black image data S1 through the cylindrical lens 84. . The laser beam Lk is deflected by the polygon mirror 82, guided to the front side of the laser printer 2, transmitted through the first scanning lens 83, and folded back by the reflection mirror 85.

  Further, the laser beam Lk is folded downward by the reflecting mirror 87, passes through the final lens 90k (for example, a toric lens), and is scanned on the surface of the photosensitive drum 36k of the black image forming unit 34k. The laser beam Lk is scanned at high speed from the left to the right (upward in the drawing in the upper drawing, hereinafter referred to as “first scanning direction”) on the surface of the photosensitive drum 36 k by the rotation of the polygon mirror 82.

  LDc is directed to one deflection surface (the same deflection surface as LDk) of the polygon mirror 82 located obliquely above from the lower position of LDk, and the laser light Lc modulated based on the cyan image data S1 passes through the cylindrical lens 84. Are arranged so as to be emitted. The laser beam Lc is deflected by the same deflection surface as that of the laser beam Lk, guided to the front side of the laser printer 2, transmitted through the first scanning lens 83, folded back by the reflection mirrors 88 and 89, and further reflected by the reflection mirror 91. It is turned downward and passes through the final lens 90c (for example, a toric lens for correcting the tilting of the polygon mirror 82) to be scanned on the surface of the photosensitive drum 36c in the cyan image forming unit 34c. The laser beam Lc is scanned at high speed along the first scanning direction on the surface of the photosensitive drum 36 c by the rotation of the polygon mirror 82.

  The LDm is arranged side by side behind the LDk, and is directed to one deflection surface (a deflection surface adjacent to the deflection surface to which the LDk and LDc are directed) of the polygon mirror 82 that is located slightly downward from the upper position. Laser light Lm modulated based on the image data S 1 is emitted through a cylindrical lens 84. The laser beam Lm deflected by the polygon mirror 82 is guided to the rear surface side of the laser printer 2 (in a direction substantially opposite to LDk and LDc), passes through the second scanning lens 86, and is folded forward by the reflection mirrors 92 and 94. It is folded downward by the reflecting mirror 96, passes through the final lens 90m (for example, toric lens), and is scanned on the surface of the photosensitive drum 36m of the magenta image forming unit 34m.

  Then, the laser beam Lm is rotated from the right to the left on the surface of the photosensitive drum 36m by the rotation of the polygon mirror 82 (downward on the paper surface in the upper drawing, opposite to the laser beams Lk and Lc. Hereinafter, referred to as “second scanning direction”. ).

  LDy is directed to one deflection surface (same deflection surface as LDm) of the polygon mirror 82 located obliquely above from the lower position of LDm, and the laser light Ly modulated based on the yellow image data S1 passes through the cylindrical lens 84. Are arranged so as to be emitted. The laser beam Ly deflected by the polygon mirror 82 is guided to the rear surface side of the laser printer 2, passes through the second scanning lens 86, is folded back by the reflecting mirror 98, and is folded downward by the reflecting mirror 100, and the final lens 90 y ( For example, the surface of the photosensitive drum 36y of the yellow image forming unit 34y is scanned through the toric lens).

  The laser beam Ly is scanned at high speed along the second scanning direction on the surface of the photosensitive drum 36y by the rotation of the polygon mirror 82. The first scanning lens 83, the second scanning lens 86, the final lens 90, the reflection mirrors 85, 87, 88, 89, 91, 92, 94, 96, 98, and 100 are supported and fixed in the housing 80. Has been.

  Also, the housing 80 is provided with a first BD (Beam Detect) sensor 101 as an example of the first detection means of the present invention and a second BD sensor 102 as an example of the second detection means of the present invention. ing. The first BD sensor 101 is provided in the irradiation range of the laser beam Lk deflected by the polygon mirror 82, and is provided at a position outside the range through which the laser beam passes through the first scanning lens 83. The laser beam Lk that does not pass through the lens 83 can be received.

  The second BD sensor 102 is positioned outside the image forming area on the surface of the photosensitive drum 36k within a range in which the laser beam Lk deflected by the polygon mirror 82 passes through the first scanning lens 83. It is provided at a position for receiving the laser beam Lk. Specifically, the first BD sensor 101 and the second BD sensor 102 are respectively disposed on the left inner wall surface and the front inner wall surface of the housing 80. As will be described later, with reference to the timing at which the first BD sensor 101 receives light, scanning start timing (writing start in the main scanning direction) on each photosensitive drum 36 not only for the laser beam Lk but also for the laser beams Lc, Lm, and Ly. (Timing) is decided.

  Further, a converging lens 99 is provided in the optical path where the laser beam Lk is deflected by the polygon mirror 82 and reaches the first BD sensor 101. The converging lens 99 has a plane that is symmetrical with respect to the optical axis in the direction in which the laser beam Lk is scanned (hereinafter referred to as the main scanning direction). The converging lens 99 converges the laser light Lk traveling toward the first BD sensor 101 on the first BD sensor 101. As will be described later, even if thermal expansion occurs in the converging lens due to temperature changes, the detection time of the first detection means serving as a reference does not vary with temperature because it is symmetrical in the main scanning direction. Therefore, even if the laser beam L passes through the converging lens, it is possible to correct with high accuracy.

  As shown in FIG. 3, the control unit 106 includes a video controller 108 as an example of a correction unit of the present invention, an engine controller 110, and a memory 112 as an example of a storage unit of the present invention. . The video controller 108 receives image data S1 from, for example, a terminal device (not shown) that is communicably connected to the laser printer 2 and develops it into bitmap data, and generates a video signal S2 for image formation.

  The video controller 108 also outputs a first BD signal S3 output at the first light reception timing when the first BD sensor 101 receives the laser light Lk, and a second light reception timing when the second BD sensor 102 receives the laser light Lk. To receive the second BD signal S4 output.

  The video controller 108 and the engine controller 110 perform serial communication so that information can be transmitted and received. The engine controller 110 receives LDk to LDy corresponding to each color of the scanner unit 48 in accordance with the video signal S2 from the video controller 108. To drive.

  The memory 112 stores a data table created in advance as an example of correspondence information of the present invention. The data table includes a detection time difference that is a time difference between the second light reception timing of the second BD signal S4 and the first light reception timing of the first BD signal S3, and the scanning start timing of the laser light L as correction data corresponding thereto. Correction data for canceling out each scanning width deviation amount is stored.

  The video controller 108 detects a detection time difference, which is a time difference between the second light reception timing of the second BD signal S4 and the first light reception timing of the first BD signal S3, and corresponds to the actually detected detection time difference. The scanning start timing and scanning width deviation amount of the laser beam L are derived from the correspondence table, and each video signal S2 is engineed at the timing when the scanning start timing of the laser beam L and the scanning width deviation are corrected so as to cancel out the deviation amount. To the controller 110.

The first BD sensor 101, the second BD sensor 102, and a third BD sensor 201 and a fourth BD sensor 202, which will be described later, together with the video controller 108 constitute a detection unit of the present invention.
[Laser light drive control during image formation]
Next, drive control of the laser beam L during image formation will be described. FIG. 4 is a time chart showing driving of the first BD sensor (BD1 in the drawing) 101, the second BD sensor (BD2 in the drawing) 102, LDk, and LDm at a certain reference temperature T1. In the figure, each LD is in an off state at a low level, and each laser beam L is turned on at a high level to emit a laser beam L, or in a “writing” state, the laser beam L is emitted based on image data. It means that it is in a state where emission is possible. For BD1 and BD2, this means that the laser beam L is received at a high level.

  The third from the top in FIG. 4 is a time chart for LDk. The controller 106 once drives the LDk before reaching the rotational position where one deflection surface of the polygon mirror 82 deflects the laser beam Lk emitted from the LDk to scan the photosensitive drum 36k. The control unit 106 receives the first BD signal S3 output when the laser beam Lk is received by the first BD sensor 101, so that the laser beam Lk is received by the first BD sensor 101. The received first light receiving timing is recognized.

  Thereafter, the controller 106 scans the laser beam Lk in the first scanning direction (see FIG. 2), and the video controller 108 receives the second BD signal S4 output by receiving the light by the second BD sensor 102. Thus, the second light receiving timing when the laser beam Lk is received by the second BD sensor 102 is recognized. Then, the video controller 108 calculates the detection time difference from the first light reception timing and the second light reception timing. The detection time difference corresponds to the time t1 that has elapsed from the first light reception timing to the second light reception timing. The detection time difference data is compared with the correction data of the data table in the memory 112 in a correction process described later.

  From this first light receiving timing, the video controller 108 gives black image data S2 to the engine controller 110 after a preset time t2 at the reference temperature T1, and outputs laser light Lk modulated based on the black image data S2. The LDk is driven to be controlled. As a result, the laser beam Lk is scanned (exposure) for one line for a predetermined time (predetermined scanning width W) while a blank area corresponding to t2 is secured on the photosensitive drum 36k, and then LDk. Is turned off.

  After that, each time the respective deflection surfaces adjacent to each other of the polygon mirror 82 come to a position where the laser beam Lk from the LDk can be deflected, the above-described series of operations are repeatedly executed to sequentially scan each line. With such a configuration, scanning of the photosensitive drum 36k is started from the writing start position in the main scanning direction by a predetermined width from the left end by the laser light Lk from the LDk.

  Similarly to LDk, LDc scans each line on photosensitive drum 36c based on cyan image data after time t2 from the first light receiving timing. Note that the first light receiving timing is detected in the laser light Lk. The same applies to LDm and LDy.

  The fourth chart from the top in FIG. 4 is a time chart for LDm. For the LDm using the second scanning lens 86, the control unit 106 outputs the laser beam Lm modulated based on the magenta image data S2 after the preset time t3 at the reference temperature T1 from the first light receiving timing. Drive control. As a result, the laser beam Lm is scanned by deflection on the one deflection surface of the polygon mirror 82, and scanning for one line is executed for a predetermined time while a blank area corresponding to t3 is secured on the photosensitive drum 36m. Thereafter, LDm is turned off.

  After that, each time the adjacent deflection surfaces of the polygon mirror 82 come to a position where the laser beam Lm from the LDm can be deflected, the above-described series of operations are repeatedly executed to sequentially scan each line. With such a configuration, scanning of the photosensitive drum 36m from the LDm by the laser beam Lm is started from the writing start position in the main scanning direction which is a predetermined inner side from the left end.

Similarly to LDm, LDy scans each line on the photosensitive drum 36y based on yellow image data after time t3 from the first light receiving timing.
In the present embodiment, the time t3 is set to a time obtained by adding the time for 4.5 cycles of Lk and Lc writing and the time t2 to the first light receiving timing. The 4.5 period corresponds to a time until one deflection surface of the polygon mirror 82 facing the LDk and LDc rotates to a position facing the LDm and LDy.

With the above configuration, the laser printer 2 according to the present embodiment has the same timing for starting writing by Lm and Ly and setting the timing for starting writing by Lk and Lc to the same time. The scanning start timings in the main scanning direction of the electrostatic latent images of magenta and yellow can be made uniform, and the color image can be transferred onto the paper P without any color shift.
[Correction control of laser light with temperature change]
Next, the scanning start timing and scanning width correction control of the laser light L accompanying the temperature rise in the laser printer 2 will be described using a timing chart. FIG. 5 is a time chart corresponding to FIG. 4 when the drive timing of LDk and LDm is not corrected in the state where the first scanning lens 83 and the second scanning lens 86 are expanded at the temperature T2 (T2> T1). is there.

  At the temperature T2, the first scanning lens 83 and the second scanning lens 86 in the scanner unit 48 expand compared to the reference temperature T1, and the magnification of each scanning lens changes. Therefore, the second light receiving timing at the second BD sensor 102 is shifted, and the scanning start timing and the scanning width of the laser beam L at the temperature T2 are the scanning start timing of the laser beam L at the temperature T1 on the photosensitive drum 36. Deviation occurs compared to timing and scan width. As a result, when image data of a plurality of colors is scanned with respect to each photosensitive drum 36, color misregistration occurs.

  That is, as shown in FIG. 4, the first light reception timing at the temperature T2 as shown in FIG. 5, as compared to the time t2 from the first light reception timing until the LDk starts scanning the photosensitive drum 36k at the reference temperature T1, as shown in FIG. From time t2 ′ until the LDk starts scanning the photosensitive drum 36k, the time t2 ′ is longer. Similarly, as shown in FIG. 5, LDm scans the photosensitive drum 36m from the first light receiving timing at the temperature T2, as compared to the time t3 from when the first light receiving timing starts until the LDm starts scanning the photosensitive drum 36m. The time t3 ′ until the start is longer.

  As described above, since the timing at which the laser beam L is scanned on the photosensitive drum 36 is shifted due to the temperature change, a shift occurs in comparison with the scanning start timing and the scanning width of the laser beam L on the photosensitive drum 36. It ends up. Therefore, it is necessary to control the driving of the LD in response to the temperature rise.

  As shown in FIG. 5, the control unit 106 drives the LDk once before scanning the photosensitive drum 36k with the laser beam Lk as described above, and the first BD sensor 101 and the second BD sensor 102 are driven with the laser beam Lk. Sequentially receive light. Then, the video controller 108 measures the detection time difference t1 ′ at the temperature T2 based on the elapsed time from the first light reception timing to the second light reception timing.

  Next, the video controller 108 reads from the data table stored in the memory 112 the correction data of the scanning start timing and the scanning width of the laser beam L corresponding to the detection time difference t1 ′.

  The correction data is derived in advance by experiment, and the time t2, t3 and the scan are used to cancel out the shift amount at the temperature T2 with respect to the scan start timing and scan width on the photosensitive drum 36 at the reference temperature T1. This is for correcting the width W, and is set for each detection time difference t1 ′ corresponding to a plurality of stages of temperatures and for each LDk, LDc, LDm, and LDy.

  The video controller 108 supplies the video signal S2 to the engine controller 110 at a timing according to the correction data. The engine controller 110 drives LDk, LDc, LDm, and LDy with the given video signal S2.

  At this time, the correction data of the scanning start timing of the black laser light Lk is applied to the laser light Lk at the time t2 from the first light receiving timing, and the photosensitive drum 36k is based on the black image data after the time t2k. One line is scanned above. Further, correction data for the scanning width of the laser beam for black is applied, and the number of dots in the image data is changed so as to substantially match the reference scanning width W. Thereby, the scanning start timing of the laser beam Lk on the photosensitive drum 36k is corrected, and the scanning width is corrected.

  Similarly, the correction data of the scanning start timing of the cyan laser beam is applied to the laser beam Lc, and after the time t2c from the first light receiving timing, the laser beam Lm is magenta laser beam with respect to the time t3. The scanning start timing correction data is applied to the laser light Ly, and the scanning start timing correction data for the yellow laser light Ly is applied to the laser light Ly with respect to the time t3. Scanning is performed on the photosensitive drum 36 based on the image data. Further, the correction data of the scanning width corresponding to each color is applied to each laser beam, and the scanning width W is substantially matched. t2k and t2c, and t3m and t3y may be different values or may be the same.

  Here, since the first and second BD sensors are not provided for the second scanning lens 86 unlike the first scanning lens 83, the laser beams Lm and Ly for the second scanning lens 86 are provided. The scan start timing and the scan width deviation amount are not calculated.

  However, in the present embodiment, the first scanning lens 83 and the second scanning lens 86 are in a symmetrical positional relationship within the housing 80 as described above. Therefore, the second scanning lens 86 and the first scanning lens 83 are in the same temperature state. Therefore, by referring to the correction data for the first scanning lens 83, it is possible to correct the scanning start timing and the scanning width of the laser beams Lm and Ly that pass through the second scanning lens 86.

  As described above, it is possible to satisfactorily correct the deviation of the scanning start timing and the scanning width of the laser light L accompanying the temperature change. Further, since the detection time difference in performing the correction process is derived with reference to the first BD sensor 101 that detects the laser light L that does not pass through the first scanning lens 83, the first scanning lens 83 accompanying the temperature change and It is possible to accurately correct the expansion of the second scanning lens 86. In addition, as a shift in the scan start timing, a shift in the sub-scan direction as well as the main scan direction can be corrected by correcting the scan start timing in the same manner.

  In this embodiment, an example in which the scanning start timing and the scanning width of the laser beam L are corrected has been described. However, only one of the scanning start timing or the scanning width may be corrected.

In addition, the data table in the memory 112 may store the shift amount of each color corresponding to each detection time difference in a plurality of stages, and the video controller 108 may calculate correction data from each shift amount and obtain it. Further, in the data table, the time t2k, t2c, t3m, t3y and the number of adjustment dots in the scanning width may be obtained in advance from each shift amount corresponding to each detection time difference, and these may be stored. In this case, the number of adjustment dots of zero at the time t2, t3 scanning width at the reference temperature T1 can be stored in the same manner.
[Modified example of scanner unit]
Next, a modification of the image forming apparatus to which the present invention is applied will be described. 6 and 7 are schematic views of a scanner unit 48 as a modified example. In the modification shown in FIG. 6, the third BD sensor 202 as an example of the third detection means of the present invention is arranged in the housing 80 of the scanner unit 48 so as to detect the laser light L that passes through the second scanning lens 86. Is positioned. In such a configuration, the correction processing for the scan start timing and the scan width shift accompanying the temperature change is performed as follows.

  First, the laser light Lk and Lc emitted from LDk and LDc is corrected based on the detection time difference between the first BD sensor 101 and the second BD sensor 102 as described above. On the other hand, the correction of the laser beams Lm and Ly transmitted through the second scanning lens 86 is performed based on the detection time difference calculated from the respective light reception timings of the first BD sensor 101 and the third BD sensor 202. That is, as described above, the first BD sensor 101 and the second BD sensor 102 sequentially detect the laser light Lk emitted from the LDk.

  Thereafter, the laser beam Lm emitted from the LDm after a predetermined time is deflected to the polygon mirror 82 and transmitted through the second scanning lens 86, and then detected by the third BD sensor 202. The video controller 108 detects a difference in detection time t101-102 from when the first BD sensor 101 detects the laser light Lk to when the second BD sensor 102 detects the laser light Lk, and the first BD sensor 101 detects the laser light Lk. A detection time difference t101-202 from the detection until the third BD sensor 202 detects the laser beam Lm is calculated.

  The data table stored in the memory 112 stores the scan start timing and scan width correction data of the laser beams Lk and Lc in advance corresponding to the detection time difference t101-102, and also corresponds to the detection time difference t101-202. Thus, the correction data of the scan start timing and the scan width of the laser beams Lm and Ly are stored.

  Thereafter, the video controller 108 reads the correction data in the data table corresponding to each detection time difference. Then, correction data corresponding to the detection time difference t101-102 is applied to the laser beams Lk and Lc, and the scanning start timing and the scanning width are corrected. On the other hand, correction data corresponding to the detection time difference t101-202 is applied to the laser beams Lm and Ly, and the scan start timing and scan width are corrected.

  With this configuration, the scanning start timing and the scanning width of the laser light L are corrected in consideration of the expansion of each scanning lens, so that the correction accuracy is further improved. Further, since only one BD sensor needs to be installed for the second and subsequent scanning lenses, it is more advantageous in terms of cost than the configuration of FIG.

  In addition, in the modification shown in FIG. 7, in addition to the configuration of FIG. 6, the fourth BD sensor 201 is installed at a position where the laser light L that does not pass through the second scanning lens 86 can be received. That is, similarly to the relationship of the first and second BD sensors 101 and 102 with respect to the laser beam Lk and the first scanning lens 83, the third and fourth BD sensors 201, 202 is arranged. The laser beam Lm emitted from the LDm is detected by the fourth BD sensor 201 through the convergence lens 299 without passing through the second scanning lens 86 due to the deflection by the polygon mirror 82.

  Thereafter, the laser beam Lm is scanned in the second scanning direction, passes through the second scanning lens 86, and is detected by the third BD sensor 202. If the detection time difference between the detection timing of the fourth BD sensor 201 and the detection timing of the third BD sensor 202 is calculated, the second laser beam Lk, Lc that passes through the first scanning lens 83 is corrected. The scanning start timing and the scanning width of the laser beams Lm and Ly that pass through the scanning lens 86 are corrected. Thus, if two BD sensors are provided corresponding to each scanning lens, the scanning start timing and the scanning width of the laser light L are corrected in consideration of the temperature expansion of each scanning lens. Accuracy is improved.

  At this time, since the detection time difference calculated for the correction process is derived based on the BD sensor that detects the laser light L that does not pass through the scanning lens, the expansion of the scanning lens due to the temperature change is accurately performed. It is corrected.

  In addition, various modifications can be made without departing from the spirit of the present invention. For example, in the embodiment, a polygon mirror is used as an example of a deflector, but the laser light may be deflected using a galvanometer mirror or the like.

  In the embodiment, the first and second BD sensors 101 and 102 for measuring the scanning start timing of each laser beam are used as detection means. However, the present invention is not limited to this. Alternatively, a configuration using various sensors that detect expansion of each part due to a temperature change may be used. However, the configuration of the above-described embodiment is low in cost because it is not necessary to provide a special sensor for the correction process.

  In the embodiment, in order to correct the scanning start timing and the scanning width of the laser beam L, the reference correction data is stored in the memory in the form of a data table, but is stored as a relational expression between the detection time difference and the correction amount. It may be a configuration.

  Further, in the embodiment, the detection time difference of the laser beam corresponding to one of a plurality of colors (black in the above embodiment) is referred to, and the correction is performed so as to cancel out the shift amount of the other colors. However, the present invention is not limited to this, and a configuration may be adopted in which detection means are provided in the same manner for all colors, and the amount of deviation is detected and corrected so as to cancel out. Further, the present invention can be applied to an image forming apparatus using only one color (for example, black).

  In the embodiment, the correction processing is performed in consideration of the expansion of the scanning lens. However, for more accurate correction, the correction processing is performed by changing the temperature of other lenses provided in the housing 80 or the scanner unit 48. The correction may be performed using correction data that takes into account the expansion and the change in magnification accompanying the above.

  Further, in the embodiment, the correction process of the scanning start timing of the laser beam L is performed every time scanning exposure for one line, but may be performed every time the image forming process for one sheet is completed. . Further, the correction process may be performed only when it is determined that the temperature rise has become significant, and the correction may not be performed if the temperature rise in the scanner unit 48 is within the allowable range. .

1 is a side sectional view showing a schematic configuration of a laser printer 2 as an example of an image forming apparatus of the present invention. 2 is a schematic diagram of a scanner unit 48. FIG. 3 is a block diagram showing an electrical configuration for controlling the scanner unit 48. FIG. It is a time chart which shows the drive of the 1st BD sensor 101 and the 2nd BD sensor 102, LDk, and LDm in the reference temperature T1. 5 is a time chart corresponding to FIG. 4 when the drive timings of LDk and LDm are not corrected in a state where the first scanning lens 83 and the second scanning lens 86 are expanded at a temperature T2 (T2> T1). It is the schematic of the scanner unit 48 as a modification. It is the schematic of the scanner unit 48 as a modification.

Explanation of symbols

2 Laser printer 36 Photosensitive drum 48 Scanner unit 82 Polygon mirror 83 First scanning lens 86 Second scanning lens 99,299 Converging lens 101 First BD sensor 102 Second BD sensor 108 Video controller 110 Engine controller 112 Memory 201 Fourth BD sensor 202 Third BD sensor

Claims (9)

A light source that emits laser light;
A deflector for deflecting the laser light emitted from the light source;
A photoreceptor,
In an image forming apparatus including a first scanning lens that scans and images the deflected laser light on the photosensitive member,
First detection means capable of detecting the laser beam that does not pass through the first scanning lens;
Second detection means provided at a position different from the first detection means and capable of detecting the laser light transmitted through the first scanning lens;
A detection time difference from when the laser beam is detected by the first detector among the two detectors, which changes in response to a temperature change, until the second detector detects the laser beam, and Storage means for storing correspondence information of the shift amount of the scanning start timing of the laser light on the photosensitive member, which changes corresponding to the change in the detection time difference,
A correction means for measuring an actual detection time difference between the two detection means, and correcting a scanning start timing of the laser light on the photoconductor based on the measurement result and the correspondence information;
An image forming apparatus comprising: A light source that emits laser light;
A deflector for deflecting the laser light emitted from the light source;
A photoreceptor,
In an image forming apparatus including a first scanning lens that scans and images the deflected laser light on the photosensitive member,
First detection means capable of detecting the laser beam that does not pass through the first scanning lens;
Second detection means provided at a position different from the first detection means and capable of detecting the laser light transmitted through the first scanning lens;
A detection time difference from when the laser beam is detected by the first detector among the two detectors, which changes in response to a temperature change, until the second detector detects the laser beam, and Storage means for storing correspondence information of the shift amount of the scanning width of the laser beam on the photosensitive member, which changes corresponding to the change in the detection time difference,
A correction means for measuring an actual detection time difference between the two detection means, and correcting a scanning width of the laser light on the photoconductor based on the measurement result and the correspondence information;
An image forming apparatus comprising:   In the optical path from the deflector to the first detection means, the laser beam is converged on the first detection means so that the laser beam has a plane symmetrical to the main scanning direction of the laser light with respect to the optical axis. The image forming apparatus according to claim 1, further comprising a lens. The photoconductor is provided corresponding to each image data for each color,
4. The image forming apparatus according to claim 1, wherein the correction unit corrects the scanning start timing or the scanning width of the photosensitive member of each color. 5.   A second scanning lens provided at a position symmetrical to the first scanning lens with respect to a plane that includes the rotation axis of the deflector and is perpendicular to the optical axis of the first scanning lens; Corrects the scanning start timing or scanning width of the photoconductor corresponding to the laser beam scanned by the second scanning lens based on the detection result of the laser beam scanned by the first scanning lens. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A plurality of the scanning lenses are provided,
Of the plurality of scanning lenses, one scanning lens can detect the laser light that does not pass through the scanning lens, and can detect the laser light that has passed through the scanning lens. The second detection means is arranged, and the third detection means capable of detecting the laser light transmitted through the scanning lens is arranged for the other scanning lenses,
The correction means corrects the scanning start timing or the scanning width of the laser beam transmitted through the other scanning lens on the photosensitive body based on a difference in detection time between the first detection means and the third detection means. The image forming apparatus according to claim 4.   The image forming apparatus according to claim 5, wherein a plurality of the scanning lenses are provided, and the first detection unit and the second detection unit are disposed corresponding to each of the scanning lenses.   The image forming apparatus according to claim 1, wherein the scanning lens is an fθ lens.   9. The rotating polygon mirror according to claim 1, wherein the deflector has a plurality of deflecting surfaces, and is a rotary polygon mirror that deflects the laser light incident on the deflecting surface by rotating around the rotation axis. The image forming apparatus according to any one of the above.